It is common for cabinets to have several drawers each of which may be filled with heavy files. When all drawers are closed, the mass of all the drawers is centred, and the file cabinet is very stable. However, when a drawer is pulled open, the weight of the drawer is removed from the centre, and there is a force created on the cabinet which acts away from the centre of mass of the cabinet. So long as there is sufficient weight in the remaining drawers to hold the cabinet vertical, the cabinet will not tip over. However, as more drawers are pulled open, the cabinet becomes increasingly unstable, and the likelihood of tipping increases. Tipping of a heavy file cabinet may cause serious injury to a person standing in front of the cabinet, or may cause damage to the file cabinet and its contents.
Various devices have been proposed to limit the number of drawers which can be open at the same time. For instance, in U.S. Pat. No. 4,272,138 an anti-tip device is disclosed which includes a segmented column consisting of a plurality of longitudinally extending snubber elements axially aligned in end-to-end abutting relation. The column extends adjacent to each drawer and the column, and/or the individual snubber elements are resiliently mounted within the cabinet to permit movement between a central equilibrium position and one of two opposite axially displaced positions. Each drawer carries on its side an activator rail which is disposed at right angles to the column. The tapered end of each activator rail is positioned so as to insinuate itself between two adjacent abutting snubber elements when the respective drawer is opened. The act of activator rail insinuation between adjacent snubber elements causes each of the snubber elements in the column to be displaced from a central equilibrium position to one of the two displaced positions. In their displaced positions, the snubber elements block opening of further drawers. In U.S. Pat. No. 4,637,667, a somewhat similar scheme is proposed in which a locking mechanism is also integrated into the design.
In U.S. Pat. No. 4,239,309 U-shaped hooks are provided on a vertical bar. The hooks engage the drawers and prevent them from opening when the hooks are displaced vertically. When a drawer is opened, a ramp mechanism on the side of the drawer slides the hook bar vertically engaging the remaining drawers, thus preventing any other drawer from opening.
These designs are complex, expensive to produce, and require manufacturing to precise tolerances.
Other designs rely on a set of bars disposed in a vertical channel of fixed length. In Canadian Patent 1,175,875 a set of vertical bars are provided, one of which is moved vertically upon the opening of a drawer such that no more vertical movement of any bar is possible, due to the fixed length of the channel for the bars. The movement of the bars is achieved by an independent cylindrical member disposed between the bars which is rotated by the opening of the drawer. The amount of space occupied between the bars by the member increases in its rotated state. This design depends upon accurate measurement of all the bars such that they all fit exactly in the length of the vertical channel when one drawer is opened. Further, the member must be rotated against the frictional force of both the bars above and below. U.S. Pat. No. 4,355,851 discloses a similar arrangement in which a rotating member engages a wedge disposed between the bars of a fixed length channel and forces the bars to slide until no more vertical play is present. Enough play is allowed such that only a single drawer may be opened. An excessive number of parts and close tolerances are required in both of these designs.
U.S. Pat. No. 4,429,930 has a rotating member which is attached pivotably to bars above and below the member such that rotation of the member causes vertical displacement of the bars. Again, the fixed vertical length of the channel in which the bars are located prevents further rotation of other members. This pivoting member is constructed from two different pieces, and is attached to both the bars above and below the pivot. This leaves little flexibility in the design of the pieces which fit in the channel because they are all physically linked together and complicate manufacture.